1. Field of the Invention
The present invention relates to heat removal devices and the attachment of heat removal devices to integrated circuit chips.
2. Related Art
Recent trends in chip design, toward highly integrated circuits, have necessitated special cooling techniques to accommodate high heat fluxes from integrated circuit chips. One conventional method of removing heat from the integrated circuits is to place to integrated circuits within a cooling module which either acts as a heat sink itself, or has a heat sink attached. Another conventional method of removing heat is to attach individual heat sinks to the back of the integrated circuit chips.
One method of mounting heats sinks to the backside of metalized ceramic modules is disclosed in an article entitled "FIXTURE FOR ASSEMBLING HEAT SINK TO MODULE" (IBM technical Disclosure Bulletin, Volume 23, No. 8, January 1981, Pages 3623-3624). The article describes an apparatus in which the heat sinks, modules and uncured adhesive epoxy preforms, are loaded into a fixture and held in place by guides and channels. After the heat sinks, modules and preforms have been properly placed into the fixture, a top cover is affixed thereto. By tightening studs on the top cover, springs are tightened. The springs, in turn, place a controlled force on a bar which is engaged to the bottom of the fixture. When the correct pressure has been applied between the heat sinks and the modules, the fixture is placed in a curing oven to effect the bond between the heat sink and the module with the epoxy preform.
While the above-described apparatus is suitable for attaching single heat sinks to each of a number of metalized ceramic modules, simultaneously attaching a plurality of heat sinks to the backs of integrated circuit chips mounted on a large substrate is problematic. Modern substrates are often made of glass ceramic rather than metalized ceramic (as is used in the module of the aforedescribed article). Because glass ceramic substrates are more brittle and in many instances larger than the metalized ceramic module of the aforementioned article, they are more prone to crack when pressure is applied. Further, fixtures such as the one described in the TDB article, which attempt to hold the substrate or module rigidly in place, only increase the likelihood of cracking.
Another problem, not addressed by the above described apparatus is that of removably mounting the heat sinks to the backs of the integrated circuit chips in a fast and efficient manner. Removably mounting the heat sinks is particularly important for burn in and manufacturing test operations, and presents several challenges. One such challenge, is removably mounting the heat sink in such a manner that the thermal interface between the heat sink and the chip is not degraded.
The burn in and test of apparatus using integrated circuit chips requiring high heat dissipations presents even more challenges. For example, since burn in temperatures will typically run hotter than standard operational temperatures, the margin between the functional temperature limit of the chip and the environment is greatly reduced. Thus, efficient heat extraction must be ensured. Further, since any failure in the heat sink/chip interface can cause costly chip damage, the attachment and thermal interface between the chips and the heat sinks must be secure, while at the same time be reversible so that the substrate and chips can be encapsulated into an electronic module after test.